One process for producing very small diameter fibers from thermoplastic material, such as glass, polyester, or polypropylene, is known as rotary fiberization. Apparatus for producing fibers by rotary fiberization are described in U.S. Pat. Nos. 4,046,539 and 4,627,868. These apparatus are commonly referred to as “fiberizers.”
A rotary-type fiberizer includes mechanisms for directing molten thermoplastic material, such as glass, into a rapidly rotating fiberizer spinner. The spinner has a plurality of small openings formed in its peripheral wall. The molten glass is forced out of the openings by the centrifugal force that is generated by the rotating spinner.
The fiberizer also includes an annular nozzle that surrounds the rotating spinner and is shaped to direct heated gas downwardly against the streams of molten glass that emanate from the spinner openings. The gas from the nozzle attenuates the molten glass streams into fine fibers and directs them downwardly. The fibers collectively fall from the spinner in the shape of a generally tubular column known as a veil. The fiber veil falls upon a conveyor surface that moves beneath the fiberizer. The fibers collect as a mat on the conveyor.
Normal operation of a rotary-type fiberizer generates a high-temperature, low-pressure (i.e., below ambient) zone directly beneath the fiberizer spinner. The air flow within the low-pressure zone is such that portions of the fiber veil separate from the veil and are drawn into the zone. These separated portions later flow outwardly against the veil. The separated fibers that flow outwardly from the low-pressure zone stick to the veil as chunks known as “remelt.” An excessive accumulation of remelt has a deleterious effect on the quality of the fiber mat.
Irrespective of the type of mechanism used for forming fibers of thermoplastic material, the fibers are often used in the manufacture of paper products, and it is desirable that the fibers provide in the sheet relatively high tensile strength, elongation, and energy absorption.